Acinus

acinus

[′as·ə·nəs]

(anatomy)

The small terminal sac of an acinous gland, lined with secreting cells.

(botany)

An individual drupelet of a multiple fruit.

Acinus

(1) A structural and functional unit or the terminal secretory portion of the salivary, pancreatic, lacteal, sebaceous, or other saccular (alveolar) glands. The acinus is a bubble-like formation of one or more types of gland cells situated on a basement membrane and surrounded by connective tissue, capillaries, and nerve fibers. The apexes of the cells with their microvilli are directed toward the chamber of the acinus into which the secretion is discharged.

(2) A part of the respiratory apparatus in mammals that includes a section of the lung corresponding to the branches of the terminal bronchus—that is, the bronchioles, alveolar passages, and alveoli. One pulmonary lobule consists of 12–18 acini.

Acinic cell carcinomas account for approximately 6% of all salivary gland neoplasms and are the fourth most common salivary malignant neoplasm, following mucoepidermoid carcinomas, adenocarcinoma not otherwise specified, and adenoid cystic carcinoma.

Histologically distinctive (although one of the few cases published in this location was reported as acinic cell carcinoma at intraoperative consultation),[6] the differential diagnosis with oncocytic cell tumors or other lesions of the salivary gland that can be composed at least partially by cells of granular cytoplasm, might be difficult, especially on fine-needle aspiration biopsy smears.

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